Automatic klystron peak mode adjustment



June 28, 1966 L. MANDEL 3,258,714

AUTOMATIC KLYSTRON PEAK MODE ADJUSTMENT M Muiden/v. fraf M June 28, 1966 Filed May l, 1964 L. MANDEL AUTOMATIC KLYSTRON PEAK MODE ADJUSTMENT 4 Sheets-Sheet 2 500KG/f' INVENTOR Lao/s MAA/061,

L. MANDEL June 28, 1966 AUTOMATIC KLYSTEON PEAK MODE ADJUSTMENT 4 Sheets-Sheet 5 Filed May l, 1964 555 F/q 5a,

555 F/q. 3a.

June 28, 1966 L MANUEL 3,258,714

AUTOMATIC KLYSTRON PEAK MODE ADJUSTMENT Filed May l, 1964 4 Sheets-Sheet 4 INVENTOR. C@ aa/5 MHA/@5L BY 61ML' LOQmLw/u @Ww /w *l/Mw United States Patent O 3,258,714 AUTOMATIC KLYSTRON PEAK MODE ADJUSTMENT Louis Mandel, Levittown, N.Y., assignor to the United States of America as represented by the Secretary of th Nav e lxfiiled May 1, 1964, Ser. No. 364,340

3 Claims. (Cl. 331-84) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to high frequency oscillators and in particular to an automatic system for adjustment of the peak power operating mode of such oscillators. The invention has particular application to the testing and evaluation of such oscillators and wide application to the proper adjustment of equipment employing such oscillators, as for example, radar units.

Broadband klystron oscillators including the reflex type are widely used in frequency modulation systems and it has been found as evidenced by the prior art that the reflector or repeller voltage must be altered as the resonant frequency of the associated cavity is changed. This 1s usually accomplished by means of an electrical potentiometer mechanically linked to the cavity tuning apparatus. There is in addition the problem of adjusting this voltage to obtain the maximum energy for the specic mode of operation. In general, a klystron circuit develops frequencies in excess of 1,000 mc. and thereby alleviates the requirement that the tube transit time be limited to a small fraction of the oscillation period. Basically this is accomplished by changing the velocities of various transit electrons and causing bunching The hunched electrons are made to radiate or give up their energy to a resonant element (cavity) much the same as a pendulum is caused to oscillate at a regular constant frequency when periodically activated or supplied with energy. There are many parameter variations, one such prime parameter being the reflector voltage which affect the output of a klystron and its operating mode. It is a characteristic of reflex klystron oscillators that they operate in several different reflector-voltage ranges designated as modes each mode extending over `a particular voltage excursion. Neglecting the small frequency variation there exists for each operating mode (cavity tuning excluded) a specific reflector potential at which maximum efficiency is derived from the oscillator. Additionally, the peaks of the various modes differ one another and where peak power is desired, it is necessary to operate at the peak of the highest energy mode. In order to determine such specific potentials, considerable time and expense must be eX- pended in manual adjustments, usually by a skilled operator. Further, where these klystrons are to be tested and evaluated in `a laboratory or on a so-called tube checker, and especially in the field, the peak of the mode capable of delivering maximum KF. power must be accurately and dynamically ascertained. The present invention is therefore directed to an automatic method and system for optimizing the reflector voltage of a frequency velocity-modulated oscillator.

It is an object of this invention to provide a simple, reliable, inexpensive and automatic method and system for dynamically adjusting the optimum peak power operating mode point of a high frequency velocity-modulated oscillator.

Another object of my invention is to provide a means for automatically and dynamically adjusting the reflector potential of a reflex klystron oscillator for any resonator tuning for a maximum R.F. output and which, additionalice ly, may be operated properly by those unskilled in the art.

Other objects and advantages will appear from the following description of an example of the invention, and the novel features Will be particularly pointed out in the appended claims.

In the accompanying drawings:

FIG. 1 is a graphical representation of the amplitude output of a klystron for various reflector potentials;

FIG. 2 is a block diagram of an embodiment encompassing the principles of this invention;

FIGS. 3a and 3b represent schematics of one specific embodiment made in accordance with this invention; and

FIGS. 4, 5, and 6 are illustrations of specific details of various mechanical components employed in utilizing the principles of the inventive concept.

Before commencing a description of an embodiment made in accordance with the principle of this invention certain specific characteristics of velocity-modulated klystron oscillators should be considered. To generate sustained oscillations with a klystron oscillator it is necessary to apply to the various elements thereof specific potentials, these usually being indicated by the manufacturer of the klystron tube and comprise heating, cathode and yrepeller or reflector voltages. With all the other circuit parameters held constant a variation of the reflector voltage causes the klystron to oscillate only over discrete ranges of reflector potential, which lranges are conventionally designated as modes. Now referring to FIG. 1, there is illustrated a plot of repeller potential against power or signal amplitude output of the klystron. Only four modes M1, M2, M3, and M4 have been shown and as is clear, as the reflector potential is increased, in a negative sense, the oscillator changes within any of the selected modes to produce first a minimum or no signal output, then increasing toward a maximum point approximately at the center of the mode, and then to another minimum on the opposite end. In practice, it is necessary to tune the klystron to the peak output power for the selected operating mode or for a total maximum R.F. output and in evaluating these klystron tubes in a laboratory as Well as for operational use, it is essential that they be quickly, properly and accurately tuned. To this end, it is obvious that for all the modes there exists a single optimum peak power operating point (a4) namely, that at which a maximum output (b4) is derived. It is with this end in view that by employing a system which automatically detects and adjusts the klystron reflector potential an oscillator may be readily evaluated.

In its most basic form the embodiment of the invention as illustrated in FIG. 2 contemplates a klystron vacuum tube 10 having a reflector electrode 11 and an R.F. output terminal 12. The R.F. output of the klystron 10 is rectified by detector 13 and applied to a D.C. amplifier 14 having a cathode follower output. This output is fed to the pole of a single pole-double throw switch 15 whose stationary contacts are individually connected to a pair of linear amplifiers 16 and 17 each characterized by an extremely low grid current, such as, electrometer tubes. One of these electrometers having cathode follower outputs, is designated as a reference electrometer 16. A differential amplifier 18 serves as a comparator which, in turn, controls by way of its output, and motor control 19 the activity of the motor and potentiometer assembly 20. A source of high potential 21 supplies a voltage across a potentiometer while the movable tap is connected to the reflector 11 of klystron 10 so that effectively the potential applied to the reflector is varied by the rotation of the motor.

Considering initially no R.F. output from the klystron, the D.C. amplifier is such that a portion thereof will be saturated while a D.C. voltage is passed through switch and charges capacitor 22 thereby unbalancing comparator 18 and resulting in activation of motor assembly 28 causing the voltage at the reflector to rise in a negative direction. As this voltage rises the R.F. output generated will follow the mode curves described and illustrated in FIG. 1. This RF. output will, in general, be followed by that D.C. voltage impressed across capacitor 22. The capacitor will always be charged to the highest value so that between modes its charge will remain constant until another mode exhibiting a higher peak is encountered Since the comparator is continually unbalanced, the motor will continue to rotate in the same direction and the reflector voltage increased. By providing a means to reverse the direction of rotation of the motor at some selected angular position the increase in reflector potential ceases and now begins to decrease. With a reversal in rotation the pole of switch 15 is displaced and the output applied to electrometer 17. The comparator 18 now receives at its inputs the total charge across the capacitor 22 which is related to the peak R.F. amplitude, and the amplitudes now being scanned during the change in reflector potential, When the peak R.F. amplitude is again obtained in the reversed direction, the comparator output will be balanced and thereby stop the motor and hold the reflector potential at this optimum setting.

The above description being only cursory, attention is directed to FIGS. 3a and 3b wherein one detailed embodiment of the invention is illustrated and the following explanation related thereto. The klystron tube 23 has a reflector electrode 24, a pair of buncher electrodes 25 and 26 coupled thereto, output terminal 27 and beam or cathode electrode 28. These tubes being quite conventional, no detailed description thereof is necessary. The repeller or reflector electrode 24 is supplied a negative potential via line 29 and variable resistance potentiometer 30 across whose fixed ends is a source of D C. potential 31, such as a battery or other suitable supply and whose movable tap 32 is connected to line 29. The center or movable tap 32 is physically coupled to be driven by a synchronous reversible motor 33 which has been appreciably geared down. A combination found suitable consists of a 72 r.p.m. motor geared down to 3 r.p.m., so that it could start and stop within one-half a degree of shaft rotation. The potentiometer used was capable of extremely fine reflector voltage control.

The klystron R.F. output is detected by a crystal rectifier 34 such as a CR-l type, and the rectified output thereof is applied across grid bias resistor 35 of dual triode tube 36. In the absence of any R.F. input signal (which would be negative) this left half of the tube operates as a saturated amplifier and its plate voltage is held to a minimum. Clearly in the operation of the klystron tube only two output states may exist, namely, the absence of R.F. and its presence. Considering the first of these, the minimum plate voltage at 37 is fed to the grid 38 of the right triode which is operating as a cathode follower and produces an output taken across a portion of the cathode resistance (39, 40). The polarity of an output therefore would be inverted from the amplifier input and so this tube also acts as a signal inverter. In the absence of R.F. the low level output of tube 36 is passed through diode 41 to the pole 42 of the double throw switch portion 43 of a relay. Assuming that the pole is shown for the normal deenergized relay, contact 44 picks up the signal or output and through wire 45 applies it to capacitor 46 which is connected between the grid 47 and ground of an electrometer tube 48. Diode 41 serves to prevent any discharge or leakage of the capacitor by way of the cathode follower output of tube 37. The small charge on the capacitor due to the output of the D.C. amplifier is sufficient to control the grid of the electrometer (type 5886 vacuum tube) which has an extremely low grid current characteristic thereby insuring maintenance of capacitor charge with little or no decay. A conventional low voltage supply 49 having a voltage regulator tube 50 across its output and a series current limiting potentiometer 51 therein, is connected across the filament 52 of the electrometer tube 48. In order to provide extreme linearity over an extended range the plate 53 and screen grid 54 are tied together in series with dual triode 55 which serves to control the plate voltage at tube 48 such that the voltage drop across this tube remains constant independent of changes in the A.C. supply. The grids 56 and 57 of regulator tube 55 are coupled to the movable tap of the series potentiometer 51 for adjustment. Thus the cathode follower output of the electrometer is developed across resistor 58 and grid 59 of comparator differential cathode follower tube 60.

A similar circuit exists for the other half of comparator tube 60 which includes power supply 61, electrometer tube 62 whose input grid is connected to stationary contact 63 of switch 43 and resistor 64. The follower output of tube 62 is developed across grid resistor 65 of tube 60. The cathodes 66 and 67 of comparator 60 are joined together through limiting resistors 68, 69, and balancing potentiometer 70. Connected between the cathodes are a pair of back-to-back diodes 71 which serve to protect the coil 72 of a highly sensitive relay. This relay controls the activation of normally open contact switch 73 such that when the comparator is unbalanced in either direction, pole 74 will close on stationary contact 75. The comparator circuit is easily balanced by shorting the two grids and adjusting potentiometer 70 so that no current will flow through coil 72 and thereby permit pole 74 to remain in its undeflected position.

An A.C. power source is connected with one leg at the junction 76 of synchronous reversible motor 33 windings 77 and 78 while the other leg is joined to pole 74 of switch 73 via initial start and override switch 79. Contact 75 is connected to pole 80 of switch portion 81 in its normal position in contact with the upper fixed contact 82 which, in turn, is connected to winding 70 of motor 33. The opposite switch contact 83 is joined to the other motor winding 77. Depending on which winding is cnergized, the motor shaft will be rotated in one direction or the other. Disposed across start switch 79 is series combination of a lower limit microswitch 84 and the relay coil 85 which controls the operation of switch 86. This switch is shown in its normal position, namely, grounding capacitor 46.

The relay coil 87 which forms a series loop with the A.C. source, and the parallel combination of upper limit switch 88 and switch 89 (controlled by coil 87), controls the operation of previously described switch 81. In its normal state with microswitch 88 open the coil is deenergized and the switches remain in the positions as illustrated.

FIG. 4 illustrates one possible embodiment of the motor coupling -to the potentiometer 30. The motor shaft 90 carries or is coupled at its upper end to the movable tap of potentiometer while the tap, by way of, for example, a brush connects to the reflector electrode 24 of the klystron 33. This simple arrangement permits the automatic scanning or application of a continuously varying voltage to the reflector. The motor shaft 90 also carries a disc or cam 91 which rotates therewith. Supported adjacent the disc are the upper 88, and lower 84, limit microswitches.

The disc 91 carries a pair of adjustable periphery stops 92 and 93 as shown in FIG. 5. With the motor shaft set at an angular position to supply a minimum reflector potential, the lower limit stop 93 is adjusted to engage normally closed microswitch 84 and hold it open. A simple larrangement for providing stop adjustment is shown in FIG. 6 where `the periphery of the disc is provided with a circumferential recess 95. This recess is formed with an enlarged inner portion 96 within which is carried a nut 97. The stop itself may be a knurled bolt having a thread portion 98 engaging the nut 97 so that when fully threaded therethrough will be locked in position and yet free to move circumferentially when loose. The motor in this position cannot rotate until momentary switch 79 is closed and when it does start to rotate in a counter clockwise direction stop 93 passes lower limit switch 84 and allows it to assume its normally closed state. At the same time, coil 3S is energized and ungrounds capacitor 46. This capacitor charges in accordance with the R.F. output of the klystron as the reflector voltage is gradually increased. Since the cornparator et) is continually imbalanced (even in the absence of RP. output), the motor will continue vto rotate until upper stop 92 engages the normally open upper limit switch S8. At this point the capacitor is charged up to a level dependent on the highest R.F. level output experienced for the entire rotation. Stop 92 causes switch 88 to close thereby energizing coil 87 which, in turn, closes latching switch 39 holding the relay energized and shifts pole 8G of switch 31 from contact 82 to contact 83 to reverse the direction of motor rotation. This same energization of coil 87 removes pole 42 of switch 43 from contact 44 Ito contact 63 s-o as to switch the input from the capacitor 46 and electrometer 48 to the grid of electrometer 62. The motor will continue to rotate in a clockwise direction until the reflector potential is such that the R.F. output is equal to the highest level encountered previously. At this point, the input connected through the amplifier 36 and the total charge on capacitor 46 are equal and no current will therefore flow between the comparator cathodes. Thus the relay of coil 72 will be deenergized and pole 74 of switch 73 will open thereby also rie-energizing motor 33. Relay coil S5, willhowever, remain energized since normally closed lower limit switch 34 and lead 94 are connected across the supply and thus the capacitor will remain ungrounded.

The potentiometer 3f) is now automatcally set to provide the proper reflector' voltage whereby the klystron RF. output is maximized. Since under these conditions, the motor will hold its position until the comparator is unbalanced, provision has been made by switch 99 to open the KF. klystron input. This imbalancing causes .the motor to start and continue its clockwise rotation since latchng switch holds coil S7 energized. The motor continues its rotation until lower limit switch is caused to open circuit by stop 93 at which instant the motor is deenergized as well as coil 85. With coil 85 open circuited switch 86 returns to its normal state and grounds out the capacitor 46 thus allowing for a new cycle.

An operating model constructed in accordance with the foregoing specifications is characterized by an accuracy of approximately 0.1 decibel within peak power and a dynamic range in excess of 30 decibels of power.

It should be noted that the method of practicing this invention need not be limited to the specific components, and circuitry described. The method in and of itself involves:

(l) Applying a D.C. potential to the mode control e'lement (eg. reflector) of the velocity modulated tube,

(2) Detecting the RP. output of the tube,

(3) Applying the detected output to a sensing-storage means (e.g. capacitor), while (4) Continually changing the DC. potential in one direction, then reversing the direction and (5) Comparing the stored output with that obtained in the reverse direction,

(6) Stopping the change in potential when the outputs are equal.

It will be understood that various changes in the details, materials and arrangements of parts (and steps), which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. A device for automatically adjusting the optimum operating potential of a high frequency velocity-modulated oscillator tube for the peak mode which cornprises:

(a) a rst relay having a pair of normally open contacts,

(b) a variable resistance having a movable tap,

(c) an R.F. detector amplifier having a cathode follower output,

(d) a capacitor,

(e) a pair of electrometer circuits having an input and an output, said capacitor connected to said input of one of said electrometers,

(f) a reversible motor having two windings, one for rotation in each direction and operatively coupled to said resistance to vary the position of said tap,

(g) an electrical supply for energizing said motor,

(h) a second relay having a coil, a pair of normally open latching contacts and a pair of single poledouble throw switches controlled by said coil,

(i) an electrical supply,

(j) a first series path having included therein said supply, said normally open contacts, the pole of one of said single pole-double throw switches, and each winding of said motor connected to the stationary contacts of said one of said single pole-double throw switches,

(k) a second series path having included therein said supply, said coil of said second relay, said latching contacts,

(l) the other of said single poledouble throw switches having its pole connected to the output of said arnplier detector and each of its fixed contacts to the inputs of said electrometers,

(m) a source of high voltage connected across said variable resistance,

(n) whereby when the R.F. output of said tube is applied to said amplifier detector and said movable tap electrically connected to the control element of said tube, a second traverse rotation of said tap will cease at a .position whereat the voltage at said control element will produce the peak mode of the tube.

2. The device according to claim l, further including:

(a) a normally open upper limit switch operatively coupled to said motor and said top for contact closure when a selected voltage at said tap is attained,

(b) said upper limit switch having its contacts connected across said latching contacts.

3. The device according to claim 2, further including:

(a) a normally closed lower limit switch operatively coupled to said motor and said tap for contact opening when another selected voltage at said tap is attained,

(b) said lower limit switch connected in said first series path.

References Cited by the Examiner UNITED STATES PATENTS 2,527,730 10/195() Hoglund 331-84 2,699,504 l/1955 Miller et al 334-22 X 2,745,015 5/1956 Stillman 334-22 X ROY LAKE, Primary Examiner.

I. KOMINSKI, Examiner. 

1. A DEVICE FOR AUTOMATICALLY ADJUSTING THE OPTIMUM OPERATING POTENTIAL OF A HIGH FREQUENCY VELOCITY-MODULATED OSCILLATOR TUBE FOR THE PEAK MODE WHICH COMPRISES: (A) A FIRST RELAY HAVING A PAIR OF NORMALLY OPEN CONTACTS, (B) A VARIABLE RESISTANCE HAVING A MOVABLE TAP, (C) AN R.F. DETECTOR AMPLIFIER HAVING A CATHODE FOLLOWER OUTPUT, (D) A CAPACITOR, (E) A PAIR OF ELECTROMETER CIRCUITS HAVING AN INPUT AN AN OUTPUT, SAID CAPACITOR CONNECTED TO SAID INPUT OF ONE OF SAID ELECTROMETERS, (F) A REVERSIBLE MOTOR HAVING TWO WINDINGS, ONE FOR ROTATION IN EACH DIRECTION AND OPERATIVELY COUPLED TO SAID RESISTANCE TO VARY THE POSITION OF SAID TAP, (G) AN ELECTRICAL SUPPLY FOR ENERGIZING SAID MOTOR, (H) A SECOND RELAY HAVING A COIL, A PAIR OF NORMALLY OPEN LATCHING CONTACTS AND A PAIR OF SINGLE POLEDOUBLE THROW SWITCHES CONTROLLED BY SAID COIL, (I) AN ELECTRICAL SUPPLY, (J) A FIRST SERIES PATH HAVING INCLUDED THEREIN SAID SUPPLY, SAID NORMALLY OPEN CONTACTS, THE POLE OF ONE OF SAID SINGLE POLE-DOUBLE THROW SWITCHES, AND EACH WINDING OF SAID MOTOR CONNECTED TO THE STATIONARY CONTACTS OF SAID ONE OF SAID SINGLE POLE-DOUBLE THROW SWITCHES, (K) A SECOND SERIES PATH HAVING INCLUDED THEREIN SAID SUPPLY, SAID COIL OF SAID SECOND RELAY, SAID LATCHING CONTACTS, (L) THE OTHER OF SAID SINGLE POLE-DOUBLE THROW SWITCHES HAVING ITS POLE CONNECTED TO THE OUTPUT OF SAID AMPLIFIER DETECTOR AND EACH OF ITS FIXED CONTACTS TO THE INPUTS OF SAID ELECTROMETERS, (M) A SOURCE OF HIGH VOLTAGE CONNECTED ACROSS SAID VARIABLE RESISTANCE, (N) WHEREBY WHEN THE R.F. OUTPUT OF SAID TUBE IS APPLIED TO SAID AMPLIFIER DETECTOR AND SAID MOVABLE TAP ELECTRICALLY CONNECTED TO THE CONTROL ELEMENT OF SAID TUBE, A SECOND TRAVERSE ROTATION OF SAID TAP WILL CEASE AT A POSITION WHEREAT THE VOLTAGE AT SAID CONTROL ELEMENT WILL PRODUCE THE PEAK MODE OF THE TUBE. 